198 THE CHEMISTKY OF ESSENTIAL OILS
butyric acids (which are present as natural esters) are soluble. This,
test applies to most of these artificial esters, such as ethyl oxalate, etc.
But more recently Schimmel has found that the following method
is more reliable than the use of barium salts: 10 grms. of the oil to be
examined are saponified on the water-bath for one hour with alcoholic
potash, the contents of the flask then placed in a porcelain dish, and
the bulk of the alcohol evaporated. After this the liquid is washed in
a separating funnel with about 100 c.c. water, the oily portions removed
by extraction with ether, the aqueous solution returned to the porcelain
dish, and the bulk evaporated on the water-bath. When the alka-
line solution is cooled down, it is acidified with sulphuric acid, and the
organic acids thus liberated absorbed with ether. The ethereal solution
is placed in a dish and the ether evaporated. For the purpose of re-
moving volatile acids (acetic acid) the residue is still heated for some
time on the water-bath, then cooled, and digested with ether. In this
manner a fine crystalline residue remains behind undissolved. On re-
crystallisation from a small quantity of alcohol, white crystals are
obtained, and the melting-point can be determined. On fractional
distillation the artificial esters will be found in the residues left after
distilling off the more volatile portion and will be found to have a very
high specific gravity and low refractive index. A comparison with
similar fractions of a normal oil will at once reveal the characteristic
differences.
Delphin
l
has found an artificial ester as an adulterant of lavender
oil which he believes to be the ethyl ester of the fatty acids of cocoa-
nut oil. He has also definitely identified ethyl phthalate as an adul-
terant.
The effects of some of the common adulterants on the characters of
the oil are as follows:—
Turpentine oil lowers specific gravity and solubility; further, the
rotation is affected, the laevo-rotatory French turpentine oil (D - 20°
to - 40°) raising, and the dextro-rotatory American oil (an up to + 15°).
lowering it.
Spike oil increases the specific gravity and lowers the rotation; the
solubility remains the same.
Spanish lavender oil behaves like spike oil, but has a less marked
influence on the rotation.
Eosemary oil also causes similar alterations to spike oil, but renders
the lavender oil less soluble.
All the additions mentioned above considerably reduce the ester
content.
Lavender oil is practically neutral. An acid value over about 3 in-
dicates the addtiion cf oaids, such as benzoic or salicylic added, to bring
up the apparent ester value.
Generally speaking, pure lavender oil is soluble in 2'5 to 3 volumes
of 70 per cent, alcohol at or under 20°, but old oils—and rarely even
freshly distilled oils, require up to 4 volumes for complete solubility, or
even in rare cases up to 7 volumes.^2
Oils are not infrequently found with a very high ester value, the
following being amongst those so recorded.
1
Svensk. Farm. tid. (1908), 22; (1912), 5.
* P. and E.O.R. (1914), 130; (1915), 314.